Copolymers provided by a part of the present inventors, for example, poly(ethylene glycol)-block-poly(dialkylaminoethyl methacrylate) form polymer micelle via an anionically charged polymer, and hence they are useful as carriers for anionically charged drug (cf. e.g., patent reference 1 and non-patent reference 1). They also can contribute to stabilize dispersions of colloidal gold or semiconductor fine particles, and can provide gold- or semiconductor-fixing (or encapsulating) polymer particles useful as markers or quantum dots in biological assay systems (cf. e.g., patent reference 2).
It is also known that poly(ethylene glycol) derivatives, in which poly(dialkylaminoethyl methacrylate) segment in above block copolymers is replaced with terminal mercapto groups, can be conveniently used for stabilizing dispersions of ultrafine particles of gold and semiconductors (see, for example, said patent references 2, 3 and 4 and non-patent reference 1). Furthermore, fine particles of a polymer having poly (oxyalkylene) segment, which are formed of a (meth)acrylic ester and styrene and are capable of encapsulating ultrafine inorganic particles serviceable as a marker in the polymer latex particles, are known to be stable in aqueous media and capable of suppressing non-specific adsorption of protein onto said latex particle surfaces (cf. patent reference 5). A part of the present inventors have also provided heterotelecheric polymers represented by, for example, a formula,
and copolymers of above polymers used as macromonomers, with styrene, (meth)acrylic acid or esters or amides thereof (cf. patent reference 6). These copolymers are a kind of graft polymers having PEG chains as branch polymers and, in addition to their functions achievable as graft polymers per se, can form conjugates with various biomolecules via aldehyde (O═CH—) groups at one of their terminals. They, therefore, are interesting as a biocompatible material.